The three-dimensional crystal structure of bovine Cu, Zn superoxide dismutase has been solved to 3A resolution. The backbone chain was traced and the metal ligands and their approximate geometry determined. Our major current project is extension of that work to 2A resolution in order to obtain a complete initial model of all atomic positions. Low-resolution diffractometer data are being collected on crystals of E. coli manganese superoxide dismutase, which is expected to have a very different protein structure. The crystals are P21212, a equals 47A, b equals 51A, c equals 188A, with one dimer of the enzyme per asymmetric unit. We are also analyzing the topologies and folding constraints of beta sheets in the known protein structures. BIBLIOGRAPHIC REFERENCES: J.S. Richardson, K.A. Thomas, B.H. Rubin, & D.C. Richardson, "Crystal Structure of Bovine Superoxide Dismutase at 3A Resolution: Chain Tracing and Metal Ligands", Proc. Nat. Acad. Sci. USA 72, 1349-1353 (1975). J.S. Richardson, K.A. Thomas, & D.C. Richardson, "Alpha-Carbon Coordinates for Bovine Cu,Zn Superoxide Dismutase", Biochem. Biophys. Res. Commun. 63, 986-992 (1975).